Abstract: Bio - oils production studied from heavy tar which is organic phase of pyrolysis oil using CoMo/Al2O3 catalyst in the bench scale hydrogenation process. In this experiments, hydrogenation of biomass tar were carried out in varied reaction conditions to elucidate influence of operation factors. The effect of reaction temperature, retention time, feed rate, space velocity (SV), hydrogen concentration, and catalyst loading factor on bio-oil yield, carbon content, and carbon recovery of heavy tar by catalytic conversion was investigated.